The heat can only be where the resistance is. Thus resistance at the boat plug cannot cause heat at the dock side plug. Bad connection at the dock outlet or perhaps a minor lightning strike would account for overheating damage. If the dock side plug got wet, it could oxidize resulting in high resistance connections that would in turn get hot. Ground or hot connection would have the same overheating effect, but only on that specific connection. The heat COULD conduct thermally to the other terminal, but likely the first thing to go would be the connector itself (as is apparently what failed).
Major amp draw would of course cause overheating, but why would that clear itself. One possible thought is that if the line voltage went very low, the stalled compressor motor would look esentially like a short circuit and overheat. When the voltage returned to normal, the motor would run noramlly, the current would return to normal and the issue (over current) would no longer be there.
Even so, the breaker should have tripped and shut down that load.
The more I think about it, the more I would be looking for a bad connection at the dock side plug or outlet.
One more piece of information... The resistances that you are looking for in your system are almost certainly very low. They will be too low to measure with an ohm meter. The best way to find a partial loss of continuity is to use a volt meter and measure across the suspected bad connection. If there is a relatively high voltage drop across the conection, you have likely found at least one issue. Sorry, but the definition of relatively high depends on how much current you are drawing and the size of the connector. I can't give you a better answer other that to compare with a similar connection. Even then, it is possible that both are bad. The other thing to do is to see if the connection gets thermally hot (as opposed to electrically hot). TURN THE LINE OFF BEFORE YOU TOUCH ANY LINE! (Frankly in Mexico, I would not trust it anyway. Who knows how it was wired?) Better yet use an IR non-contact thermometer and see if the immediate area is hot.
TerryMSU
